Here is the way I see it. You need to take some responsiblity for this..You must not really love your current fiance if you cheated on her. Now is a perfect time to figure out if you do really love her or are just in it for some other reason. If you tell her now, it will save you from more issues after marriage. I love my Wife and even though she yells, gripes and blows thing out of proportion occasionally, I would never think of cheating on her. Even with one of my Ex's ( I can remember one that was hot as hell) You are young and can re coupe from this easily and find a new woman. I didn't get married till almost 31 and I'm glad I waited. Most of us who are slightly older and learned from our mistakes are trying to give you the best advice. Tell your fiance, see what happens. Wait till that kid is born and get a paternity test. Move on if the current plans for marriage don't work out. Remember there are more fish in the sea. Good Luck!!